Biological Soil Crusts in the Mojave Desert, USA: Micromorphology and Pedogenesis

Abstract

Biological soil crusts (BSCs) are bio-sedimentary complexes that play critical ecological roles in arid landscapes; however, the interactions between component biota and sediments are poorly understood. A detailed micromorphological investigation of BSC development and crust microstructure in the Muddy Mountains Wilderness Area, Nevada, examined features in thin section using pétrographie microscopy, light microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. The >1800 microscopic observations were linked to crust macroscale features and soil geomorphology. Complex bio-sedimentary structures of BSCs reflect a dynamic genetic history and diverse formative processes, including: (i) stabilization and authigenic mineral precipitation; (ii) wetting-drying and expansion-contraction; (iii) dust capture; (iv) microscale mass wasting; and (v) vesicular (Av) horizon formation. A new conceptual model for hot deserts illustrates how these processes co-develop with BSC succession, during countless wet-dry cycles, to huild up pinnacle microtopography while simultaneously forming Av horizons in the bio-rich and hio-poor zones. Complex surficial and internal hio-sedimentary structures, which vary as a function of crust morphology, trap surface water for uptake hy crust organisms, while dust influx provides a source of nutrients. These phenomena influence landscape-scale water dynamics and biogeochemical cycling, increasing the availability of soil resources during times of biotic stress. Biological soil crusts uniquely facilitate the accumulation, morphology, and ecosystem function of dust and should, therefore, be considered critical agents in arid pedogenesis and landscape development.Abbreviations: BSC, biological soil crust; EPS, extracellular polymeric secretions; XPL, cross-polarized light.

Early life on land and the first terrestrial ecosystems

“…The capacity of microbes to trap and bind particles has been demonstrated for numerous underwater and subaerial environments (Gunatilaka 1975;Zhang 1992;Takeuchi et al 2001;Altermann 2008;Gradzinski et al 2010;Williams et al 2012). If microbes were responsible for much of the global dust capture, retention, and lixiviation on the early continents, recycling effects may have had profound implications for the evolution of global ecosystems through geologic time, as well as for important climatic processes, such as those rooted in atmospheric albedo variations Jickells et al 2005;Lau et al 2006).…”

Modelling the diurnal and seasonal dynamics of soil CO<sub>2</sub> exchange in a semiarid ecosystem with high plant–interspace heterogeneity

“…Moreover, we presumed structural homogeneity for the crust layer and employed a constant regime for crust processes. In reality, there may not be clear boundaries between top crust and subcrust, and even top crust itself may contain significant variations in microstructure and communities even within 1 cm (Williams et al, 2012;Raanan et al, 2016). The C sequestration of biocrust can be strongly modified by microbial communities directly (Belnap et al, 2003;Pointing and Belnap, 2012;Feng et al, 2014;Maestre et al, 2015) and through other factors, e.g.…”

“…The C sequestration of biocrust can be strongly modified by microbial communities directly (Belnap et al, 2003;Pointing and Belnap, 2012;Feng et al, 2014;Maestre et al, 2015) and through other factors, e.g. surface albedo (Chamizo et al, 2012), dew falls (Liu et al, 2006) and soil pore formation (Williams et al, 2012;Felde et al, 2014). So far, many questions remain unanswered about the mechanisms that control the colonization, adaption and succession of microbial communities and the structure function of biocrust (Pointing and Belnap, 2012).…”

La vida temprana en la Tierra y los primeros ecosistemas terrestres

“…La capacidad de los microbios para capturar y unir partículas ha sido demostrada para numerosos entornos subacuáticos y subaéreos (Gunatilaka, 1975;Zhang, 1992;Takeuchi et al, 2001;Altermann, 2008;Gradzinski et al, 2010;Williams et al, 2012). Que los microbios fueran responsables de gran parte de la captura global de polvo, retención y lixiviación en los continentes primitivos, tendría profundas implicaciones para el funcionamiento biogeoquímico y evolución de los ecosistemas globales a través del tiempo, así como para importantes procesos climáticos (i.e.…”